The present application relates to the fabrication of semiconductor structures and, more particularly to a method of removing a silicon-containing antireflective coating (SiARC) layer in a sidewall image transfer (SIT) patterning process without causing a height loss of spacers.
Sidewall Image Transfer (SIT) is a process that doubles the density of a line pattern and is thereby very important to continued silicon technology scaling. The SIT process conventionally involves a conformal deposition of a spacer material layer over a previously patterned SIT mandrel followed by etching back the spacer material layer to form spacers on the sidewalls of the mandrels. The mandrels are then removed, leaving behind only the spacers. In certain applications, a block mask including a stack of an organic planarization layer (OPL), a silicon-containing antireflective coating (SiARC) layer, and a photoresist layer is applied over the SIT spacers. The block mask is then patterned to form a blocked area and an unblocked area. The unblock area corresponds to a region where the spacer defined pattern is transferred to an underlying metal nitride hard mask layer and eventually to the substrate. Once the block mask is patterned to expose spacers in the unblocked region, the patterned SiARC layer needs to be removed before patterning the metal nitride hard mask layer using the exposed spacers as an etch mask.
However, etching the SiARC layer selective to the spacers exposed in the unblocked area can be a challenge. For example, silicon oxide formed by a low temperature in-situ radical assisted deposition (iRAD) is commonly employed as the spacer material. In such a situation, dry etches employing fluorine-based chemistry that are suitable for SiARC removal also etch the spacers because iRAD silicon oxide and SiARC have similar material properties and are etched at similar rates. This inadvertent etching of the oxide-based spacers can reduce the spacer heights. The relatively short spacers results in a poor metal hard mask etching profile, which leads to a non-uniformity during the trench and via pattering subsequently performed. As such, there remains a need to develop a novel approach that allows removal of the SiARC layer with enhanced etch selectivity relative to the silicon oxide-based spacers.